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Appl. Environ. Microbiol., May 1996, 1610-1615, Vol 62, No. 5
K Suberkropp and H Weyers
As leaves enter woodland streams, they are colonized by both fungi and
bacteria. To determine the contribution of each of these microbial groups
to the decomposition process, comparisons of fungal and bacterial
production are needed. Recently, a new method for estimating fungal
production based on rates of [(sup14)C]acetate incorporation into
ergosterol was described. Bacterial production in environmental samples has
been determined from rates of [(sup3)H]leucine incorporation into protein.
In this study, we evaluated conditions necessary to use these methods for
estimating fungal and bacterial production associated with leaves
decomposing in a stream. During incubation of leaf disks with radiolabeled
substrates, aeration increased rates of fungal incorporation but decreased
bacterial production. Incorporation of both radiolabeled substrates by
microorganisms associated with leaf litter was linear over the time periods
examined (2 h for bacteria and 4 h for fungi). Incorporation of
radiolabeled substrates present at different concentrations indicated that
400 nM leucine and 5 mM acetate maximized uptake for bacteria and fungi,
respectively. Growth rates and rates of acetate incorporation into
ergosterol followed similar patterns when fungi were grown on leaf disks in
the laboratory. Three species of stream fungi exhibited similar ratios of
rates of biomass increase to rates of acetate incorporation into
ergosterol, with a mean of 19.3 (mu)g of biomass per nmol of acetate
incorporated. Both bacterial and fungal production increased exponentially
with increasing temperature. In the stream that we examined, fungal carbon
production was 11 to 26 times greater than bacterial carbon production on
leaves colonized for 21 days.
Copyright © 1996, American Society for Microbiology
Application of Fungal and Bacterial Production Methodologies to Decomposing Leaves in Streams
Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama 35487-0206
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